Pine Trees Help Reconstruct a Long-Ago Drought By JUSTIN GILLIS Daniel Griffin/Laboratory of Tree-Ring Research A cross section of a bristlecone pine with its annual growth rings. As they struggle to understand modern climate change, scientists have long realized the importance of reconstructing past climate variability. That’s the only way to gain a sense of perspective, to understand how anomalous modern climate events are or aren’t. Yet the field of “paleoclimatology” has been plagued by controversy, with reconstructions of past temperatures emerging as a particular target for climate-change contrarians. The essential problem, of course, is that the temperature record that tells us the Earth is warming goes back only to about 1850, when observation stations systematically began keeping such data, and most other climate records are even shorter and spottier. Reconstructi...